Vaporizer for Liquefied Petroleum Gas and Vaporizer

ABSTRACT

The invention relates a fuel vaporizer for a motor vehicle operated with liquefied petroleum gas. The vaporizer has a vaporization space, which has an inlet for liquid fuel and an outlet for vaporized fuel, and a second space, which together with the vaporization space forms a heat exchanger and forms an inlet for cooling water from an internal combustion engine and an outlet. The inlet and the outlet of the second space are connected via a line bypassing the second space. A switching valve is disposed at the inlet of the second space so as to introduce a cooling water flow selectively into the second space or the line. The vaporizer also has an electric heater for heating the second space.

The invention relates to a vaporizer for liquefied petroleum gas.

Liquefied petroleum gas used for motor vehicles is frequently also referred to as autogas or LPG. Motor vehicles operated with this gas generally comprise a fuel tank, in addition to a liquefied petroleum gas tank, so that the internal combustion engine of the vehicle can be selectively operated with liquefied petroleum gas or gasoline. The pressurized liquefied petroleum gas present in the tank is fed in gaseous form to the internal combustion engine via a vaporizer and pressure regulator. Because the gas cools off drastically during vaporization, the vaporizer is heated with cooling water from the internal combustion engine.

Such motor vehicles are typically operated with gasoline at first when starting to drive and switch to LPG operation at a later time when the cooling water has heated up.

Liquefied petroleum gas is considerably less expensive than gasoline and produces fewer harmful substances. This applies in particular to high-consumption cold running phases of the engine.

It is therefore an object of the present invention to show a way of how the advantages of liquefied petroleum gas as a fuel for vehicles can be utilized even better.

SUMMARY OF THE INVENTION

According to the invention, the cooling water flow used during normal operation for heating a vaporizer chamber can be redirected via a bypass line and a water volume enclosed in the vaporizer can be electrically heated. In this way, the vaporizer can be operated even when the engine is cold, and a vehicle can thus be switched from gasoline operation to LPG operation at an earlier time, or the engine can even be started with liquefied petroleum gas.

In a method according to the invention, the temperature of the cooling water flow can be monitored and used as a criterion for switching between the two operating states of the vaporizer. It is possible to switch to normal operation, in which the vaporizer chamber is heated by a cooling water flow heated by the engine, as soon as the cooling water temperature, or engine temperature, has exceeded a predefined threshold value. It is also possible to switch to normal operation when a predefined time period has passed since the engine was started.

In the fuel vaporizer according to the invention, a section of a cooling water line, which together with a vaporization space forms a heat exchanger, can be decoupled from a cooling water flow by a switching valve and the cooling water flow can be redirected to a bypass line. The part of the cooling water system that can be decoupled by the switching valve forms a second chamber in the fuel vaporizer. An electric heater is disposed in this second chamber so that water contained therein can be heated as needed so as to be able to operate the vaporizer even when the cooling water is cold.

BRIEF DESCRIPTION OF THE DRAWING

Further details and advantages of the invention will be described based on an exemplary embodiment with reference to the attached drawing. In the drawing:

FIG. 1 is a schematic illustration of an exemplary embodiment of a fuel vaporizer for a motor vehicle operated with liquefied petroleum gas.

DETAILED DESCRIPTION

FIG. 1 shows a fuel vaporizer for a motor vehicle operated with liquefied petroleum gas. The fuel vaporizer has a vaporization space comprising an inlet 6 for liquid fuel and an outlet 7 for vaporized fuel. The fuel vaporizer additionally has a second space 1 for cooling water. Together with the vaporization space, the second space 1 forms a heat exchanger and comprises an inlet for cooling water of an internal combustion engine and a cooling water outlet. An electric heater 5, which is shown schematically in FIG. 1, is disposed in the second space.

The inlet and outlet of the second space 1 are connected to each other by a bypass line 2, which bypasses the second space. A switching valve 3 is located at the start of the bypass line. A switching valve 4 is disposed at the end of the bypass line 2. The switching valves 3, 4 can be used to direct a cooling water flow 10 selectively through the bypass line 2 or through the second space 1 of the vaporizer containing the electric heater 5.

In a first operating state, the vaporizer is heated by the electric heater 5 while a cooling water flow 10 bypasses the second space 1 via a bypass line 2. By means of the two switching valves 3, 4, it is advantageously achieved that, during operation of the electric heater 5, only a relatively small amount of water has to be heated, which is to say the amount of water enclosed in the space 1 between the switching valves 3, 4. The water heated by the electric heater 5 in turn heats the vaporization space, because the vaporization space and the second space 1 containing the electric heater 5 form a heat exchanger.

In a second operating state the cooling water flow heated by the engine of the vehicle is conducted through the space 1 containing the heater 5 and the bypass line is closed by the switching valves 3, 4. The heater 5 is shut off in the second operating state. The vaporization space is then heated via the cooling water flow 10 by the waste heat of the engine.

The fuel vaporizer 1 shown comprises a temperature sensor 8 for monitoring the temperature of the cooling water flow 10 supplied to the switching valve 3. This temperature sensor 8 can be integrated in the switching valve 3 or can be disposed upstream thereof.

The temperature sensor 8 can be connected to a control unit, which is not shown and actuates the switching valves 3, 4. If the cooling water temperature measured by the temperature sensor 8 exceeds a predefined threshold value, the cooling water flow 10 can be conducted through the second space 1. In this case, the control unit preferably shuts the electric heater 5 off. If the temperature measured by the temperature sensor 8 exceeds a predefined threshold temperature, a switch is thus made from the first operating state to the second operating state.

A temperature sensor 9 is provided for monitoring the temperature present in the second space 1. The temperature sensor 9 is preferably disposed in the second space 1, but can also be attached to a heat-conducting outside wall of the second space 1. The temperature sensor 9 can likewise be connected to a control unit. It is also possible, however, to use the temperature sensor 9 only to protect against overheating and to use it, for example, as a temperature controller. In the simplest case, the temperature sensor 9 can be designed as a bimetallic switch that is connected in series to the electric heater 5.

In the exemplary embodiment shown, the second space 1 of the fuel vaporizer containing the heater 5 is disposed around the vaporization space. A heat exchanger, however, can also be implemented by other arrangements, for example a helical design of the second space 1 around a cylindrical vaporization space, or a vaporization space in the form of a bundle of pipes that is guided through the second space 1.

The electric heater 5 may comprise a ceramic PTC element to protect it from overheating. PTC heating elements, for example such based on barium titanate, exhibit a sudden increase in the electric resistance at a critical threshold temperature and thus provide intrinsic protection from overheating.

REFERENCE NUMERALS

-   1 Second space -   2 Bypass line -   3 Switching valve -   4 Switching valve -   5 Heater -   6 Inlet -   7 Outlet -   8 Temperature sensor -   9 Temperature sensor -   10 Cooling water flow 

1. A fuel vaporizer for a motor vehicle operated with liquefied petroleum gas, comprising: a vaporization space having an inlet for liquid fuel and an outlet for vaporized fuel; a second space, in combination with the vaporization space, forming a heat exchanger and having an inlet for cooling water from an internal combustion engine and an outlet, the inlet and the outlet of the second space being connected via a line bypassing the second space; a switching valve disposed at the inlet of the second space, for introducing a cooling water flow selectively into the second space or the line; and an electric heater for heating the second space.
 2. The fuel vaporizer according to claim 1, further comprising a temperature sensor for monitoring the temperature of a cooling water flow supplied to the switching valve.
 3. The fuel vaporizer according to claim 1, wherein the outlet of the second space and the line are connected by a further switching valve.
 4. A fuel vaporizer according to claim 1, wherein the heater contains a ceramic PTC element.
 5. A fuel vaporizer according to claim 1, further comprising a temperature sensor for monitoring the temperature present in the second space.
 6. A fuel vaporizer according to claim 2 further comprising a control unit connected to the temperature sensor for actuating the switching valve in order to conduct a cooling water flow through the second space when the cooling water temperature, measured by the temperature sensor, exceeds a predefined threshold value.
 7. The fuel vaporizer according to claim 6, wherein the control unit is operative for shutting off the electric heater when the switching valve is brought into a switching state in which a cooling water flow is conducted through the second chamber. 